1. Field of The Invention The present invention relates to an improved apparatus for stacking, transferring and bundling sheet material in signature form as received from a conveying device.
2. Description of the Prior Art
It is known in the graphic arts that sheet materials such as newspapers, books, printed cartons and the like emerge from a printing operation in a serial, partially overlapping shingled or signature form. In the conventional arrangement, a stream of sheets, for example in the form of newspapers, is collected on a conveyor which receives the sheets from the printing press, cutter or folder and which moves the sheets to a stacker. Stackers are commonly employed in the printing industry for collecting and aligning the signatures. The stacker receives the sheets in serial form from the conveyor and forms a neat aligned stack which is easy to bundle together for removal and transportation. Many stacking arrangements are known in the art as exemplified by U.S. Pat. Nos. 2,933,314; 4,361,318; 2,933,314 and 4,463,940 which are incorporated herein by reference. U.S. Pat. No. 4,463,940 describes a commonly used stacker having an upswept arcuate array of rollers sequentially engaging signatures with crusher rollers and opposed endless timing belts which are compression mounted by the series of rollers. U.S. patent application Ser. 08/009,774 shows an improved stacker which is preferred for use by this invention and such is incorporated herein by reference. Folded, overlapped signatures exiting from the end of a printing press are stream conveyed along a horizontal course leading to the stacker. The stacker changes the stream path from horizontal to vertical. The signatures are initially crushed between rollers to compact them and to exhaust entrapped air. The stream of shingled signatures is thereafter passed between top and bottom conveyors which form a compression zone of the stacker and which maintains the signatures fully compressed during their transition from a horizontal stream to a vertical stream. Upon leaving the compression zone the stream of signatures has an upward thrust. They are then stopped, engage a receiver and form a growing, stack of the signatures on a horizontal conveyor belt. The stack takes the shape of an ever enlarging right rectangular parallelepiped. The horizontally stacked product is then bundled, that is, compressed and/or tied and placed onto a skid, pallet or into a box for shipment. Bundling apparatus are also well known in the art. In this regard, see U.S. Pat. Nos. 3,982,749; 3,825,134; 3,739,924 and 3,635,463. Bundlers compress the stack of signatures to remove any remaining compressed air and wrap a tight band of strapping material around the stacks for boxing or palletizing.
It has been a problem in the art to provide an efficient and effective means of transferring stacks of signatures from the horizontal exit conveyor of the stacker to the bundling station. While the stacking and bundling operations in and of themselves are routinely automated, the transfer from the stacker to the bundler has been a labor intensive task. In the past, a stacked pile of paper materials such as printed signatures has been assembled on flat tables after processing by the stacker conveyors. End boards, or pieces of plywood the same size as the signatures are placed at either end of the formed bundle and then the signatures and end boards are moved by hand to another portion of the table for compression and bundling. Such an operation has many disadvantages since such hand movement of the stacked signature requires considerable strength and effort and movement of the stack along the table tends to abrade and damage the lower edges of the signatures which are in contact with the table. Additionally, there is a disruption of signature alignment into an uncompressed group of signatures. One solution is embodied in the commercially available Baldwin Stobb DH series equipment. U.S. Pat. Nos. 4,723,883 and 5,022,813 have suggested other possible solutions which include a stacker to bundler shuttling apparatus. The equipment is in the form of a table having pivotable tracks which carries a platform on a rolling shuttle for picking up and transferring a collection of signatures from the stacker to a position on the table for compression and bundling. While this equipment considerably alleviates the effort required to move a stack from one position to another, it has rather severe drawbacks. The means for lifting the signatures is provided by pivoting the tracks on which the wheels of the shuttle are engaged. These systems are disadvantageous since a large force and a substantial mechanism are necessary to raise not only the collection of signatures, but also the platform, platform truck and the track. Furthermore, as the length of the machine is extended, the difference in the amount of lift provided near the pivot end as opposed to the opposite end begins to become extreme. Also, the structural integrity of the track with possible binding due to bending moments and other forces comes into question and requires special care and added costs. The present invention improves on the forgoing apparatus whereby a two part bundle transfer vehicle is provided which eliminates the need for a pivoted track. Rails can be provided that essentially are structural members of the basic frame construction. As a result, much less force is needed to raise the stack. In addition, since weight is much less of a consideration, much sturdier rails and transfer vehicles can be used. Special care against track binding is eliminated. In a most preferred embodiment, a bundle transfer vehicle comprises a two part construction. It has a first rolling element portion comprising wheels or other friction reducing means, rolls or otherwise traverses horizontally back and forth along a stationary horizontal rail. It further has a second elevator portion which rides on the first portion and may be raised and lowered under the stack of signatures. This arrangement provides significant advantages. The length of travel is of very little concern, especially since the rails are structural members. All motion is level motion, thus easing powered bundle transfer vehicle motion. Lifting motion is uniform, that is straight up, regardless of the length of the rail or the position of the apparatus along the length of the rail. It is easier to install multiple streams since one can raise or lower the signatures in a stream independently of the rails. In addition, the cost of manufacture is much less. These and other features, advantages and improvements will be in part discussed and in part apparent to one skilled in the art upon a consideration of the detailed description of the preferred embodiment and the accompanying drawings.